1. Field of the Invention
The present invention relates to the field of optical power meters which measure optical power and more particularly to a combined optical power and noise meter which also measures optical noise.
2. Description of the Prior Art
U.S. Pat. No. 4,889,985, entitled Combined Optical Power Meter and Receiver, issued to Bryan E. Allsop, Allen W. Mabbitt and Kevin K. Smith on Dec. 26, 1989, teaches a combined optical power meter and receiver in which the optical power meter retains high sensitivity and the optical receiver retains high bandwidth. A single photodiode provides current for both the optical power meter and the optical receiver. A first operational amplifier is configured as an integrating transimpedance amplifier having a current input which is referenced to a reference voltage and receives current from one port of the photodiode. A second operational amplifier is configured as a transimpedance amplifier having a current input which is referenced to ground and receives current from the other port of the photodiode. In this manner, a bias voltage is developed across the photodiode to decrease the capacitance and increase the operational speed of the receiver. A second material photodiode is provided which is shielded from the input light source is coupled to the current input of the first transimpedance amplifier. The polarity of the second photodiode is such that a path exists for the leakage current of the first photodiode, which decreases the sensitivity of the optical power meter to thermal variations in leakage current.
U.S. Pat. No. 4,904,035, entitled Coupling Device for Guiding a Light Beam, issued to Siegfried Heckmann and Johannes Rybach on Feb. 27, 1990, teaches a coupling device for guiding a light beam sent through an end portion of an optical waveguide to the light-sensitive surface of a photodiode of a measuring instrument, in particular, an optical power meter, comprising an absorbing aperture associated with the end face of the optical waveguide, and having an aperture which widens conically towards the light-sensitive face of a photodiode, the aperture plate facing the end face of the optical waveguide with its side where the diameter of said aperture is smallest but slightly larger than the diameter of said end face of the optical waveguide. A device of simple construction and having substantially no reflection is obtained in that the light beam is directed straight to the light-sensitive surface of the photodiode.
U.S. Pat. No. 4,908,567, entitled Power supply System for an Optical Inspection Apparatus, issued to Robert H. Welker and Ken Smith on Mar. 13, 1990, teaches an optical inspection apparatus consists of an explosion-proof light projector and a viewing periscope. In one embodiment, an external power source connects to an explosion-proof housing protectively enclosing a lamp. In another embodiment, the lamp, batteries, and a circuit are included within the explosion-proof housing, providing a fully portable, self-contained and explosion-proof light projector. A viewing periscope is provided for examination of meter tubes, tanks vessels and other enclosed machinery. An explosion-proof connector is also disclosed providing an explosion-proof and thermally resistant interface between a light source and a fiberoptic light guide. A timing circuit disclosed prolonging the operation time of the light projector on one charge of the battery.
U.S. Pat. No. 4,927,266, entitled Optical Signal Generating Apparatus and Optical Power Meter Calibrating System Using the Same, issued to Itsuo Sugiura, Yutaka Nishida, Kaoru Ito and Toshiyuki Ozaki on May 22, 1990, teaches in an optical signal generating apparatus output light from a light source driven by a light source driver is externally output from an optical receptacle through a variable optical attenuator. An output monitor unit can be detachably connected to the optical receptacle through an optical connector. When an absolute level of the output light is to be set, a CPU compares a set value from an output level setting unit with an output value from the output monitor unit and controls the variable optical attenuator and the light source driver so that a comparison error becomes zero. The CPU maintains the above control of the variable optical adjuster and the light source driver so that the light is output to be the desired level set by the output level setting unit even after the output monitor unit is disconnected from the optical receptacle including the timing at which the comparison error becomes zero. An optical power meter calibrating system includes the above optical signal generating apparatus as a stabilized light source. In the optical power meter calibrating system, in place of the output monitor unit, a standard optical power meter and an optical power meter to be calibrated are selectively, detachably connected to perform calibration.
U.S. Pat. No. 4,749,275, entitled Optical Power Meter with Automatic Switching of Photodetectors having Different Wavelength Sensitivity Characteristics, issued to Teiichi Shimomura and Kunio Ishikawa on June 7, 1988, teaches an optical power meter system which includes a chopper with a semicircular total reflection mirror along an incident light path, two photo-detectors of different characteristics of wavelength sensitivity, and a comparator for comparing the levels of the photo-detection signals derived from the two photo-detectors and for outputting the optical detection signal of a higher level. The photo-detectors are positioned in a first path of the light passing through the chopper and a second path of the light reflected by the chopper, respectively. The comparator may be replaced by an adder for adding the photo-detection signals derived from the two photo-detectors.
U.S. Pat. No. 4,865,446, entitled Laser Power and Energy Meter, issued to Takemi Inoue and Ichiro Yokoshima on Sept. 12, 1989, teaches a laser power and energy meter has a target surface provided with at least one pin hole for passing a small portion of the laser beam impinging thereon and further has a light detector positioned in the path of the laser light passing through the pin hole. The target surface is moved horizontally and vertically to cause the laser beam to scan the target surface and the center of the laser beam is aligned with the center of the target surface.
U.S. Pat. No. 4,864,218, entitled Method of Compensating for Frequency Errors in Noise Power Meters, issued to Bernard W. Leake and Andrew C. Davidson on Sept. 5, 1989, teaches a method of measuring and compensating for measurement frequency inaccuracies encountered when measuring noise power of a device under test within a desired calibrating frequency range. The method includes sweeping a frequency synthesizer through a frequency range which includes the desired measurement frequency range. Power is measured for different synthesizer frequencies with the noise power meter set to the desired frequency range. Alternatively, the frequency synthesizer may be set to the desired measurement frequency and the noise power meter swept through a range including the desired measurement frequency. The resulting power measurements show the frequency range within which the noise power meter actually measured power. The difference between the desired measurement frequency range and the actual measurement frequency rang is the measurement frequency error which may be corrected using a frequency conversion stage to displace test signals by the amount of the measurement frequency error before they are sent to the noise power meter.